The present invention relates to injection-blow molding machines and is concerned more particularly with a machine in which the parison and the container are removed from their respective molds without splitting the molds.
It is now a well known and widely used industry practice to form containers and the like in injection-blow molding processes in which a parison is initially formed by injecting a settable plastic over a parison pin in an injection mold and then transferring the parison in a softened state to a blow mold where the parison is expanded by air to the final form of the container. One such injection-blow molding machine is disclosed in U.S. Pat. No. 3,816,050 entitled Neckring Mechanism for Plastic Injection Blow Molding Machine having the same assignee as the present invention. In the patented machine, both the injection and blow molds split along a central plane passing through the vertical axis of the parison and container. During a molding operation, the mold halves must be clamped together or "locked up" with clamping pressures sufficient to prevent the formation of flashing on the vertical side walls of the finished article where labels or identifying information are usually placed or printed.
One approach to the flashing problem is utilized in the present invention and consists of designing the blow mold so that the parting plane of the machine is situated perpendicular to the vertical container axis at a portion of the blown container other than the vertical sides and thus a smooth vertical surface is provided where labels or printing are applied. In such design, the blow mold need not split along a vertical plane to release containers having transverse cross sections equal to or smaller than the mouth of the mold and several additional advantages are obtained. With a non-splitting mold, more cavities of simpler construction can be located within a given space and, therefore, a more compact machine is produced. Furthermore, a more uniform temperature distribution within the mold can be obtained since the number of pieces defining the mold cavity can be reduced. It is also easier to develop a more uniform wall thickness in the finished container since air displaced from the cavity during a blowing operation can be more easily controlled. In general, the molding machine and its operation are improved by the use of a non-splitting mold.
In U.S. Pat. No. 3,694,124, an injection-blow molding machine is disclosed in which the axes of the mold cavities and the finished container are located perpendicular to the basic parting line of the molding machine; however, the blow mold is nevertheless formed by mold segments which split during each cycle of the machine to permit the blown container to be extracted. Therefore, although the general arrangement of the machine is similar to that suggested above, the general problems of flashing or mold impressions on the finished particle are not addressed.
It is, accordingly, a general object of the present invention to provide injection-blow molding machine in which the blow mold as well as the injection mold are non-splitting mold components.